JP2005222812A - Manufacturing method of electrode for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the output of a fuel cell by previously mixing carbon particles with alcohol and improving wettability of the surfaces of the carbon particles before preparing electrode paste by mixing the carbon particles with cation exchange resin. <P>SOLUTION: Carbon particles containing alcohol are prepared (a first process), the carbon particles containing alcohol and a cation exchange resin solution are mixed to prepare a mixture A containing the cation exchange resin solution, the alcohol, and the carbon particles (a second process). A solvent is removed from the mixture to obtain a mixture B containing the cation exchange resin and the carbon particles (a third process). Cations of a catalyst metal are adsorbed on pair ions of the cation exchange resin in the mixture B obtained in the third process (a fourth process). And then, the cations of the catalyst metal adsorbed in the fourth process are chemically reduced (a fifth process). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a fuel cell electrode.

2. Description of the Related Art Conventionally, the following methods for producing fuel cell electrodes are known (see, for example, Patent Document 1 and Patent Document 2). That is, (1) First, carbon particles and an alcohol solution of a cation exchange resin are mixed and then dried to form a mixture of carbon and a cation exchange resin (mixture forming step). (2) Then, the mixture is immersed in a salt solution containing a catalyst metal cation, and the cation is adsorbed on the counter ion of the cation exchange resin contained in the mixture (cation adsorption step). (3) Thereafter, the cation is reduced to make the cation a catalytic metal (reduction step).
In the above production method, in the mixture forming step (1), the mixture is formed into a sheet shape. Alternatively, in the mixture forming step (1), the mixture is powdered, and cation adsorption is performed in this powder state. After reduction, a solvent is added to the powder to form a slurry, which is formed into a sheet.
JP 2000-12041 A JP 2003-257439 A

However, in this manufacturing method, carbon particles with low wettability on the surface and an alcohol solution of a cation exchange resin are mixed, so that the alcohol solution of the cation exchange resin adheres unevenly to the surface of the carbon particles. Was.
As a result, the distribution of the sulfonic acid groups of the cation exchange resin on the surface of the carbon particles becomes non-uniform, and the distribution of the catalyst ions (for example, Pt ²⁺ ) adsorbed on the sulfonic acid groups is also non-uniform. The dispersion of was inadequate.

Therefore, the dispersion of the catalyst metal produced by reducing the catalyst ions is also insufficient, and the ideal condition is that the smallest possible catalyst metal particles are adhered to the carbon particle surface with a uniform distribution. In other words, catalyst particles considerably larger than the above were unevenly adhered to the surface of the carbon particles.
Therefore, the output of the fuel cell using the electrode manufactured by the above-described manufacturing method is not always sufficient.
The present invention has been completed based on the above circumstances, and an object thereof is to improve the output of a fuel cell.

  The inventors of the present invention have made extensive studies to develop a method for producing an electrode for a polymer electrolyte fuel cell that can solve such problems. As a result, before the electrode paste is prepared by mixing the carbon particles and the cation exchange resin, the carbon particles and the alcohol are mixed in advance to improve the wettability of the carbon particle surface, thereby improving the carbon particle surface. It has been found that the dispersibility of the catalyst metal is remarkably improved and the output of the fuel cell is improved. The present invention has been made based on this finding.

That is, the method for producing an electrode for a fuel cell according to claim 1 includes a first step of producing carbon particles containing alcohol, the carbon particles containing alcohol obtained in the first step, and a cation exchange resin. A second step of mixing the solution to obtain a mixture A containing a cation exchange resin solution, an alcohol and carbon particles; and the cation exchange resin solution, the alcohol and carbon particles obtained in the second step. A third step of obtaining a mixture B containing a cation exchange resin and carbon particles by removing the solvent from the mixture A containing, and a mixture containing the cation exchange resin and carbon particles obtained in the third step A fourth step of adsorbing the cation of the catalytic metal on the counter ion of the cation exchange resin in B; and a cation of the catalytic metal adsorbed on the counter ion of the cation exchange resin in the fourth step. A fifth step of biological reduction is a method for manufacturing a fuel cell electrode, characterized in that through the.
The reason why the output of the polymer electrolyte fuel cell is improved by the electrode manufactured by the manufacturing method of the present invention is estimated as follows.

First, the conventional manufacturing method is demonstrated using the schematic diagram of FIGS. In this production method, first, carbon particles and an alcohol solution of a cation exchange resin are mixed and then dried to form a mixture of carbon and a cation exchange resin (mixture formation step). At this time, the surface of the carbon particles 1 to be mixed is not treated at all and has low wettability, so that the cation exchange resin 3 adheres unevenly to the surface as shown in FIG. It is guessed. Note that the cation exchange resin 3, (in the figure, -SO 3 ^_-) cation exchange groups such as shown in FIGS. 1 and 2 are believed to cluster portion 5 which assembled is present. In this cluster portion 5, it is considered that a collection of cation exchange groups in a ring shape is arranged so as to be stacked in the thickness direction of the resin layer, and the whole is arranged in a cylindrical shape (FIG. 2 shows the cylindrical shape). A cross-sectional view of the cluster portion 5 is shown).

Next, this mixture is immersed in a salt solution containing a cation of a catalytic metal to adsorb the cation (cation adsorption step). Then, as shown in FIG. 2, it is considered that the cation (for example, Pt ²⁺ ) of the catalyst metal is adsorbed on the cluster portion 5 (note that FIG. 2 shows 1 of the cation exchange resin 3 portion of FIG. This is an enlarged schematic diagram. Thereafter, when the cations are reduced, it is considered that the catalytic metal particles 7 are supported on the surfaces of the carbon particles as shown in FIG.

Next, the manufacturing method of this invention is demonstrated. In the following description, the diameter of the carbon particles is the same as that of the conventional one shown in FIGS. 1 to 3, and the amount of the cation exchange resin attached to the carbon particles is also the same as that shown in FIGS. The same amount as the conventional one of No. 3.
In this manufacturing method, carbon particles and alcohol are mixed to produce carbon particles containing alcohol (first step). By this step, alcohol adheres to the surface of the carbon particles and the wettability of the surface is improved.

  Next, the carbon particles containing the alcohol obtained in the first step and the cation exchange resin solution are mixed to obtain a mixture A containing the cation exchange resin solution, the alcohol and the carbon particles (second product). Process). At this time, since the surfaces of the carbon particles 1 to be mixed are already wetted with alcohol and have high wettability, the cation exchange resin 3 uniformly adheres to the surfaces as shown in FIG. Presumed to be. In addition, the thickness of the cation exchange resin layer on the surface of the carbon particles is thinner than that of the conventional one.

Next, the solvent is removed from the mixture A containing the cation exchange resin solution, the alcohol and the carbon particles obtained in the second step to obtain a mixture B containing the cation exchange resin and the carbon particles (third Process). As a method for removing the solvent, methods such as heat drying, reduced pressure drying, and ultrasonic irradiation can be used. The mixture of the cation exchange resin and the carbon particles obtained here contains almost no solvent or alcohol of the cation exchange resin solution. Further, in the obtained mixture, a cation exchange resin film is formed on the surfaces of the carbon particles and the mesopores of the carbon particles.
Next, the cation of the catalyst metal is adsorbed on the counter ion of the cation exchange resin in the mixture B containing the cation exchange resin and carbon particles obtained in the third step (fourth step).
Here, in the cluster portion 5, it is assumed that the cation exchange groups gathered in a ring shape as described above are arranged so as to be stacked in the thickness direction of the resin layer. In the method, it is considered that the number of cation exchange groups per one cluster portion 5 is smaller than that prepared by the conventional method (see FIG. 2) as shown in FIG. Therefore, the number of cations adsorbed per cluster portion 5 is also reduced.

Next, the cation of the catalyst metal adsorbed on the counter ion of the cation exchange resin in the fourth step is chemically reduced (fifth step). Here, since the number of cations adsorbed per cluster portion 5 is smaller than that by the conventional manufacturing method, the catalytic metal particles produced by reducing the cations as shown in FIG. 7 is also considered to have a smaller particle size than the conventional one.
Moreover, in this manufacturing method, as shown in FIG. 4, the cation exchange resin 3 is uniformly attached to the surface of the carbon particle 1, and the cluster portion 5 is also more dispersed on the carbon particle surface than the conventional method. The catalytic metal particles 7 produced by reduction of the cations adsorbed on the cluster portion 5 are also highly dispersed on the carbon particle surfaces (see FIG. 6).

From the above, according to the production method of the present invention, the particle diameter of the catalytic metal particles 7 supported on the carbon particle surface can be made smaller than that prepared by the conventional method, and the surface of the carbon particle is highly advanced. It can be in a state of being dispersed.
Therefore, even if the electrode by the manufacturing method of the present invention is provided with catalyst metal particles having the same weight as the electrode manufactured by the conventional method, the diameter of the catalyst metal particles 7 is small. The surface area increases dramatically compared to the conventional one. Furthermore, the catalytic metal particles are uniformly dispersed on the surface of the carbon particles, and the electrode reaction occurs uniformly on the surface. Therefore, it is estimated that the output of the fuel cell using the electrode by the manufacturing method of the present invention is improved as compared with the fuel cell using the electrode by the conventional manufacturing method.

Hereinafter, each process will be described in detail in order.
First, the first step of mixing carbon particles and alcohol to produce carbon particles containing alcohol will be described.
The carbon particles are not particularly limited, and any of furnace black, acetylene black, lamp black, thermal black, and channel black can be used. However, the carbon particles are high in reduction of the catalyst raw material compound (for example, metal salt, metal complex). For example, when a platinum group metal compound is used, carbon black such as Denka Black, Vulcan XC-72, Ketjen Black EC, and Black Pearl 2000 is preferable.

The specific surface area of the carbon particles is not particularly limited, but is preferably 50 to 1500 m ² / g, and more preferably 50 to 1000 m ² / g.
Thus, when the specific surface area is 50 to 1500 m ² / g, the catalyst metal particles can be supported in a highly dispersed state on the surfaces of the carbon particles.
That is, when the specific surface area of the carbon particles is smaller than 50 m ² / g, the number of places where the catalytic metal particles are supported on the surface of the carbon particles is reduced.
For this reason, there is a possibility that the catalyst metal particles are not dispersed and localized.
On the other hand, if the specific surface area of the carbon particles is larger than 1500 m ² / g, the surface area may be too large to uniformly coat the carbon particle surfaces with the cation exchange resin. That is, there is a possibility that the cation exchange resin necessary for covering the entire surface is insufficient.
The specific surface area means a BET specific surface area and can be measured using, for example, Shimadzu Corporation, Micromeritex, Jenimi 2370.

  The alcohol is not particularly limited, and a well-known alcohol can be used. However, a monovalent alcohol having 4 or less carbon atoms has high affinity with the cation exchange resin, and the carbon particle surface is wetted with the cation exchange resin solution. It is preferable for improving the property. In particular, at least one alcohol selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol, 1-butanol, and 2-butanol is preferable.

The mixing ratio of the carbon particles and the alcohol is not particularly limited, and the carbon particles containing alcohol are in a slurry form when the alcohol ratio is high, and are in a powder form when the alcohol ratio is low. However, the ratio of 5 to 20 parts by weight of alcohol with respect to 1 part by weight of carbon particles is preferable, the ratio of 5 to 15 parts by weight of alcohol with respect to 1 part by weight of carbon particles is more preferable, It is particularly preferable to mix the alcohol at a ratio of 5 to 10 parts by weight.
When the amount is less than this range, the alcohol hardly spreads over the entire surface of the carbon particles, and the improvement of the wettability of the carbon particle surface by the alcohol tends to be insufficient. On the other hand, if it exceeds this range, the viscosity of a mixture containing a cation exchange resin, alcohol and carbon particles, which will be described later, becomes too low, and its handling (for example, molding into a sheet) tends to be difficult.

Next, the second step of obtaining the mixture A containing the cation exchange resin solution, the alcohol and the carbon particles by mixing the carbon particles containing the alcohol obtained in the first step and the cation exchange resin solution. Will be explained.
The cation exchange resin used in this step is not particularly limited, and a known cation exchange resin can be used. For example, perfluorosulfonic acid ion exchange resin, styrene-divinylbenzene sulfonic acid type cation resin. An ion exchange resin can be used.

  In addition, when mixing a cation exchange resin solution with the carbon particle containing alcohol, an alcohol solution is preferable. In addition, it does not specifically limit as alcohol at the time of preparing the solution of a cation exchange resin, Although a well-known thing can be used, C4 or less monohydric alcohol is preferable. This is because the monovalent alcohol solution having 4 or less carbon atoms has high affinity with the surface of the carbon particles wetted by the first step. In particular, at least one alcohol selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol, 1-butanol, and 2-butanol is preferable. Moreover, when setting it as a solution, the solution density | concentration is not specifically limited.

In addition, when mixing the cation exchange resin solution and the alcohol-containing carbon particles, the ratio of the weight of the carbon particles to the solid content weight of the cation exchange resin is not particularly limited, but preferably 8: 2 to 2: 8 (weight ratio), more preferably 7: 3 to 3: 7 (weight ratio), and particularly preferably 4: 6 to 6: 4 (weight ratio). When the weight ratio of the cation exchange resin is larger than this range, the contact between the carbon particles is hindered by the cation exchange resin, so that the electron conduction path tends to be blocked, and as a result, the resistance inside the electrode increases. This is because the performance may be degraded.
On the other hand, if the weight ratio of the cation exchange resin is smaller than this range, the cation exchange resins are not connected to each other (because they are in a separated state), so that the proton transmission path tends to be blocked. Therefore, the supply of protons is hindered and the electrode reaction does not proceed, and the performance may be reduced.

Next, the third step of obtaining the mixture B containing the cation exchange resin and the carbon particles by removing the solvent from the mixture A containing the cation exchange resin solution, the alcohol and the carbon particles obtained in the second step. Will be described.
In this step, for example, the mixture A of the cation exchange resin solution, alcohol and carbon obtained in the second step is applied onto a support (for example, a polymer sheet such as PTFE), and dried from this mixture. Therefore, by removing the solvent, a sheet made of a mixture of a cation exchange resin and carbon can be obtained. This sheet can be used as it is as a fuel cell electrode (electrode comprising a catalyst layer) through a fourth step (adsorption) and a fifth step (reduction) described later.
In order to form a mixture of a cation exchange resin solution, alcohol and carbon into a sheet, an arbitrary forming method such as a method of rolling with a roller, a method of applying using a doctor blade, or a method of spraying with a spray is used. Can be used.
The thickness of the dried sheet is not particularly limited, but is preferably 5 to 100 μm, more preferably 10 to 80 μm, and particularly preferably 20 to 50 μm. If the thickness is larger than this range, the salt solution does not penetrate into the sheet in the fourth step described later, and the catalyst metal may not be supported on the surface of the carbon particles inside the electrode.
This is because if the thickness is less than this range, there are too few catalyst metal particles that can be supported on the sheet, and there is a tendency that stable fuel cell performance (cell performance) cannot be guaranteed.

In the third step, it is not always necessary to form a mixture of a cation exchange resin solution, alcohol and carbon into a sheet. In the third step, the solvent is removed from the mixture, and the cation exchange resin is removed. And a mixture of carbon and carbon may be used. In this case, adsorption and reduction of cations are performed in a powder state, and then a solvent such as alcohol is added to the obtained powder to form a slurry, which is formed into a sheet.
In the case of drying in a powder form, for example, a mixture of a cation exchange resin solution, alcohol and carbon may be simply dried, or suction filtration may be used in combination. Specifically, a mixture of a cation exchange resin solution, alcohol and carbon may be once subjected to suction filtration and further dried. Further, suction filtration and drying may be repeated.

  Next, the fourth step of adsorbing the cation of the catalytic metal to the counter ion of the cation exchange resin in the mixture B containing the cation exchange resin and carbon particles obtained in the third step will be described in detail. To do. The mixture of the cation exchange resin and the carbon particles may be in a sheet form or a powder form.

Here, the catalyst metal is not particularly limited, but a metal having high catalytic activity for electrochemical oxygen reduction reaction and hydrogen oxidation reaction is suitable, for example, platinum, rhodium, ruthenium, iridium, palladium, osnium. Platinum group metals such as and their alloys are preferred.
In particular, as a catalyst metal used for the anode-side electrode, an alloy containing platinum metal, for example, an alloy containing platinum and ruthenium is preferable because of its high resistance to CO poisoning (carbon monoxide resistance).
Further, an alloy containing at least one element selected from the group consisting of magnesium, aluminum, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, silver and tungsten, and a white metal metal is used as a catalyst metal. When used as, it is possible to obtain the effects that the amount of platinum metal used can be reduced, the CO poisoning resistance is improved, and a high activity for oxygen reduction reaction is obtained.
In addition, as a salt containing a cation of a catalytic metal, a salt of a metal salt or a complex (complex salt), particularly [Pt (NH ₃ ) ₄ ] X ₂ , [Pt (NH ₃ ) ₆ ] X ₄ , [Rh ( NH ₃ ) ₆ ] X ₃ , [Ru (NH ₃ ) ₆ ] X ₃ , [Ir (NH ₃ ) ₆ ] X ₃ , [Pd (NH ₃ ) ₄ ] X · H ₂ O, [Os (NH ₃ ) ₆ ] A salt of an ammine complex that can be represented as X ₃ or the like is preferred. In addition, a plurality of types of salts may be mixed and used, or a double salt may be used. For example, by using a mixture of a platinum compound and a ruthenium compound, formation of a platinum-ruthenium alloy can be expected by reduction.
The solvent of the salt solution is basically water, but other solvents may be mixed.
The concentration of the salt solution is not particularly limited.

Next, the fifth step of chemically reducing the cation of the catalytic metal adsorbed on the counter ion of the cation exchange resin in the fourth step will be described.
The reduction method in the fifth step is not particularly limited, and may be a well-known method such as a chemical reduction method using a reducing agent, a gas phase reduction method using hydrogen gas or a hydrogen-containing gas, or an inert gas containing hydrazine. A gas phase reduction method or the like is used. The reducing conditions (reducing agent type, reducing pressure, reducing agent concentration, reducing time, reducing temperature, etc.) can be appropriately selected depending on the type of cation to be adsorbed.

The fuel cell electrode is manufactured through the above steps. When the mixture of the cation exchange resin and carbon is formed into a sheet in the third step, after the reduction in the fifth step, the sheet is removed from the catalyst layer carrying the catalyst metal. It becomes the electrode for fuel cells. In the third step, when the mixture of the cation exchange resin and carbon is dried to form a powder, after reduction in the fifth step, a solvent such as alcohol is added to the powder to form a slurry. The slurry is formed into a sheet shape to obtain a fuel cell electrode comprising a catalyst layer.
The amount of catalyst metal supported on the fuel cell electrode is not particularly limited and can be controlled by the concentration of the salt solution or the rate of introduction of cation exchange groups in the cation exchange resin. For example, the amount of catalyst metal supported Can be 0.01 to 0.05 mg cm ⁻² .

Further, using the above-described fuel cell electrode, for example, a fuel cell is assembled as follows.
That is, with the fuel cell electrodes (catalyst layers) stacked on both sides of the cation exchange membrane, hot pressing is performed at a temperature equal to or higher than the glass transition point of the cation exchange membrane to form a membrane-electrode assembly (MEA). electrode-assembly).
A gas diffusion layer made of carbon fiber or the like is laminated on both sides of the membrane-electrode assembly, and a separator (bipolar plate) is adhered and laminated on both outer sides via gaskets to obtain a fuel cell.
The cation exchange membrane used for the production of the membrane-electrode assembly is not particularly limited, and is a well-known polymer electrolyte membrane, for example, a fluororesin ion exchange membrane having a sulfonic acid group (for example, perfluorosulfone). Acid-type cation exchange membranes) and styrene-divinylbenzene-based sulfonic acid-type cation exchange membranes can be used.

  When the electrode produced by the production method of the present invention is used, the output of the fuel cell is improved.

Hereinafter, the present invention will be described in more detail with reference to examples.
1. Example 1
First, carbon particles (Vulcan XC-72 (Cabot) 1.0 g) and isopropyl alcohol (10 g) were mixed using a hybrid mixer (HM-500, Keyence) to obtain carbon particles containing alcohol.
Next, 6.7 g of a cation exchange resin solution (a solution of Alfrich, catalog no. 27470-4 Nafion 5 wt% solution heated to 80 ° C. to obtain a Nafion 10 wt% solution) was added to 11 g of the slurry. Mixing was performed using a mixer (HM-500, Keyence) to prepare a mixture of a cation exchange resin, alcohol and carbon particles. In this mixture, the weight of carbon particles: weight of the solid content of the cation exchange resin = 60: 40.

Next, the mixture of the cation exchange resin, alcohol and carbon particles is applied to a polymer sheet (PTFE sheet, film thickness 25 μm) and then naturally dried to obtain a mixture of the cation exchange resin and the carbon particles. A catalyst layer (thickness 30 μm) of a platinum unsupported electrode was obtained. The catalyst layer of the platinum-unsupported electrode was immersed in an aqueous solution (60 ° C.) of 50 mmol / l [Pt (NH ₃ ) ₄ ] Cl ₂ for 6 hours, whereby [Pt (NH ₃ ) ₄ ] ²⁺ was ^added to the catalyst layer. Adsorbed.
Next, this electrode was washed with deionized water three times and then immersed in deionized water (60 ° C.) for 1 hour. Thereafter, the electrode was dried in a dryer (60 ° C.) for 24 hours. Furthermore, [Pt (NH ₃ ) ₄ ] ²⁺ adsorbed on the catalyst layer was reduced in a hydrogen atmosphere of 0.15 MPa and 180 ° C. for 6 hours to deposit platinum on the catalyst layer. Thus, a platinum carrying electrode (platinum carrying amount 0.035 mg cm ⁻² ) was produced. This electrode was punched to a size of 5 cm × 5 cm (25 cm ² ), and then hot-pressed (95 ° C., 232 kg cm ⁻² , held for 3 minutes) on both sides of the cation exchange membrane (Nafion 115, manufactured by DuPont). By bonding, an electrode-cation exchange membrane-electrode assembly was produced. Further, the joined body was immersed in sulfuric acid (0.5 mol l ⁻¹ , 80 ° C.) for 1 hour, and then immersed in deionized water (80 ° C.) for 1 hour, whereby the electrode was not reduced [Pt ( NH _{3) 4]} was eluted ^2+. A gas diffusion layer (Dainippon Ink, Auspon E02, thickness 0.2 mm) made of carbon fiber or the like is laminated on both sides of the joined body, and a separator (bipolar plate) is interposed on both outer sides via gaskets. Are closely stacked to form a fuel cell A.

2. Comparative Example 1
First, 13.4 g of a cation exchange resin solution (manufactured by Aldrich, 5% by weight Nafion 5 wt% solution of catalog no. 27470-4) was added to 1.0 g of carbon particles (Vulcan XC-72 (Cabot)), and a hybrid mixer (HM -500, Keyence Corporation) to prepare a mixture of the cation exchange resin solution and the carbon particles. In this mixture, the weight of carbon particles: weight of the solid content of the cation exchange resin = 60: 40.

Next, the mixture of the cation exchange resin solution and the carbon particles is applied to a polymer sheet (PTFE sheet, film thickness 25 μm) and then naturally dried to obtain a mixture of the cation exchange resin and the carbon particles. A catalyst layer (thickness 30 μm) of the platinum unsupported electrode was obtained. Using this catalyst layer, a fuel cell B was produced in the same manner as in Example 1. That is, the catalyst layer of the platinum-unsupported electrode is immersed in an aqueous solution (60 ° C.) of 50 mmol / l [Pt (NH ₃ ) ₄ ] Cl ₂ for 6 hours, whereby [Pt (NH ₃ ) ₄ ] ^{2+ is} added to the catalyst layer. Was adsorbed.

Next, this electrode was washed with deionized water three times and then immersed in deionized water (60 ° C.) for 1 hour. Thereafter, the electrode was dried in a dryer (60 ° C.) for 24 hours. Furthermore, [Pt (NH ₃ ) ₄ ] ²⁺ adsorbed on the catalyst layer was reduced in a hydrogen atmosphere of 0.15 MPa and 180 ° C. for 6 hours to deposit platinum on the catalyst layer. Thus, a platinum carrying electrode (platinum carrying amount 0.035 mg cm ⁻² ) was produced. This electrode was punched to a size of 5 cm × 5 cm (25 cm ² ), and then hot-pressed (95 ° C., 232 kg cm ⁻² , held for 3 minutes) on both sides of the cation exchange membrane (Nafion 115, manufactured by DuPont). By bonding, an electrode-cation exchange membrane-electrode assembly was produced. Further, the joined body was immersed in sulfuric acid (0.5 mol l ⁻¹ , 80 ° C.) for 1 hour, and then immersed in deionized water (80 ° C.) for 1 hour, whereby the electrode was not reduced [Pt ( NH _{3) 4]} was eluted ^2+. A gas diffusion layer (Dainippon Ink, Auspon E02, thickness 0.2 mm) made of carbon fiber or the like is laminated on both sides of the joined body, and a separator (bipolar plate) is interposed on both outer sides via gaskets. Are closely stacked to form a fuel cell B.

3. Electrochemical platinum surface area measurement According to well-known electrochemical measurement methods (for example, the new edition electrochemical measurement method (Electrochemical Society edition (1988)), the amount of hydrogen desorption electricity of the electrodes of fuel cell A and fuel cell B QμC was measured, and this value was divided by the electrode area to obtain the hydrogen desorption amount of electricity Q ₁ μC per electrode unit area, and Q ₁ μC was divided by 210 μC / cm ² , and this value was further divided into the electrode unit area. The active surface area A (cm ² mg ⁻¹ ) per platinum unit weight was calculated by dividing by the amount of platinum supported per unit (see formula below).
A = Q ₁ / (210 · platinum amount per unit electrode area)

In addition, argon gas was supplied to the working electrode side, and hydrogen gas was supplied to the counter electrode side under a humidified condition of 25 ° C., respectively.
As a result of the measurement, the electrochemically active surface area of the working electrode of the fuel cell A (Example 1) was 1051.4 cm ² / mg. On the other hand, the electrochemically active surface area of the working electrode of the fuel cell B (Comparative Example 1) was 914.3 cm ² / mg. Thus, the electrode of the fuel cell A has a larger active surface area per unit weight of platinum than the electrode of the fuel cell B. The catalyst metal platinum is smaller in the electrode of the fuel cell A than the electrode of the fuel cell A. And it was presumed that it was highly dispersed.

4. Measurement of Current-Voltage Characteristics of Fuel Cell The current-voltage characteristics of fuel cell A and fuel cell B were measured. Air humidified at 80 ° C. is supplied to the cathode side, and hydrogen gas humidified at 80 ° C. is supplied to the anode side to obtain an oxygen utilization rate of 40% and a hydrogen utilization rate of 80%, and an operating temperature of 80 ° C. .

The results are shown in the graph of FIG. The cell voltage of the fuel cell A at 300 mA cm ⁻² was 0.597 V, which was 47 mV higher than that of the fuel cell B.
From the above results, it was found that the output of the fuel cell was improved when the fuel cell electrode produced by the production method of the present invention was used.

5. Examination of the kind of alcohol Next, the kind of alcohol at the time of preparing the carbon particle containing alcohol was examined. Here, instead of isopropyl alcohol in Example 1, methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol, 1-butanol, 1-hexanol, 1-octanol, and ethylene glycol were used. Considered the case.
A catalyst layer (electrode) was produced in the same manner as in Example 1 except that these alcohols were used.
And the moldability at the time of obtaining the catalyst layer (electrode) of a platinum unsupported electrode by apply | coating the mixture of a cation exchange resin solution, alcohol, and a carbon particle to a polymer sheet and evaluating the platinum surface area was evaluated. The results are shown in Table 1.

  From Table 1, when any alcohol was used, the moldability of the catalyst layer was good. However, when a monovalent alcohol having 4 or less carbon atoms (methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol, 1-butanol) is used, an alcohol having 5 or more carbon atoms is used. As a result, the active surface area per unit weight of platinum was larger than that of (1-hexanol, 1-octanol) or divalent alcohol (ethylene glycol). This is presumed to be because monohydric alcohol having 4 or less carbon atoms has high affinity with the cation exchange resin and is excellent in improving the wettability of the carbon particle surface to the cation exchange resin solution. .

6. Examination of mixing ratio of carbon particles and alcohol Next, the mixing ratio of carbon particles and alcohol when preparing carbon particles containing alcohol was examined.
Here, when mixing carbon particles and isopropyl alcohol using a hybrid mixer to obtain carbon particles containing alcohol, the mixing ratio of the carbon particles and isopropyl alcohol was changed.
A catalyst layer (electrode) was produced in the same manner as in Example 1 except that the mixing ratio was changed.
And the moldability at the time of obtaining the catalyst layer (electrode) of a platinum unsupported electrode by apply | coating the mixture of a cation exchange resin solution, alcohol, and a carbon particle to a polymer sheet and evaluating the platinum surface area was evaluated. The results are shown in Table 2.

When the amount of alcohol was 5 to 20 parts by weight with respect to 1 part by weight of the carbon particles, the active surface area per unit weight of platinum was particularly large.
This is presumed to be because the wettability of the carbon particle surface is remarkably improved within this range. On the other hand, when the amount of alcohol exceeds this range, the viscosity of the mixture of the cation exchange resin solution, the alcohol and the carbon particles becomes too low, so that it is difficult to form the sheet.

Schematic diagram of conventional carbon particles Enlarged view of FIG. Schematic diagram of conventional catalyst-supported carbon particles Schematic diagram of carbon particles produced by the production method of the present invention Enlarged view of FIG. Schematic diagram of catalyst-supported carbon particles by the production method of the present invention Graph showing the current-voltage characteristics of a fuel cell

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Carbon particle 3 ... Cation exchange resin 5 ... Cluster part 7 ... Catalyst metal particle

Claims (1)

A first step of producing carbon particles containing alcohol;
A second step of mixing the carbon particles containing the alcohol obtained in the first step with a cation exchange resin solution to obtain a mixture A containing the cation exchange resin solution, the alcohol and the carbon particles; ,
A third step of removing the solvent from the mixture A containing the cation exchange resin solution and the alcohol and carbon particles obtained in the second step to obtain a mixture B containing the cation exchange resin and the carbon particles;
A fourth step of adsorbing the cation of the catalytic metal to the counter ion of the cation exchange resin in the mixture B containing the cation exchange resin and carbon particles obtained in the third step;
And a fifth step of chemically reducing the cation of the catalytic metal adsorbed on the counter ion of the cation exchange resin in the fourth step, and a method for producing an electrode for a fuel cell.

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